Gastric juice acidity was examined in 131 patients with gastric ulcer. In 31 (23.7%) patients it appeared to be high, in 57 (43.5%)-normal, in 42 (32.8%)-low. In 28.6% cases the pepsin concentration was high, in 26.5%-normal, in 44.9% - low. In elder patients, patients with cardial ulcer, plural and combined ulcers, big size ulcers, long-term ulcer anamnesis the rate of low acidity increases. Among patients with unsatisfactory results of conservative treatment 15.8% had high acidity and 38.7% low acidity. Low acidity is an unfavorable prognostic factor.